Subscription television system



5 Sheets-Sheet 1 J. E. BRIDGES SUBSCRIPTION TELEVISION SYSTEM Feb. 11, 1958 .Filed June 11,1954

lzelm. 11, 1958 J. E. BRIDGES 2,823,253

` SUBSCRIPTION TELEVISION SYSTEM Filed. June 11. 19514V y 5 sne'ets-shet z QD lob-4 Generator" E l f7 From Diode Circuit *ToRese f 67 or |47 monnecion BY MM FTIG. 6

HIS ATTORNEY.

Feb. 11, 1958 J. E. BRIDGES 2,823,253

SUBSCRIPTION TELEVISION SYSTEM Filed June 11, 1954 5 Sheets-Sheet 5 f2 fsufl Resef-- f7 f3 Time *aXJEZ O D.

` JACK E. BRIDGES i INVENTOR.

HIS ATTORNEY.

FEG. 3g

Feb. 11, 1958 J. E; BRIDGES I SUBSCRIPTION TELEVISION SYSTEM Filed June 1l, 1954 www?. 025-22m JACK E. BRIDGES INVENTOR. (/M j HIS ATTORNEY.

Feb. ll, 1958 J. E. BRIDGES 2,823,253

SUBSCRIPTION TELEVISION SYSTEM Filed June 11, 1954 s sheets-sheet 5 JACK E. BRIDGES INVENToR..

H'IS ATTORNEY.

' 2,823,253 SUBSCRIPTION TELEVISION SYSTEM Jack E. Bridges, Franklin Park, lll., assignor to Zenith Radio Corporation, a corporation of Illinois Application June 11, 1954, Serial No. 436,121 18 Claims. (Cl. 1785.1)

Since the invention may be practiced in either a subi scription television transmitter or receiver, the term encoding 1s used herein in its generic sense to encompass either coding at the transmitter or decoding at the receiver.

In the above-mentioned copending application, there is specifically described and claimed a subscription television system in which during each of a series of recurring mode-determining intervals a combination of.

code signal components, individually having a predetermined identifying characteristic such as frequency and collectively representing a code pattern, is developed at the transmitter. The code signal components, which are preferably randomly-sequenced and randomly-appearing within each combination, are segregated from one another in suitable filters for application over assigned in-` put circuits to a transposition mechanism. The transposition mechanism selectively establishes a multiplicity of circuit connections between the input circuits and a plurality of output circuits, which are connected to various input circuits of a multi-stable actuating mechanism such as `a bi-stable multivibrator. With this arrange-` ment, the several code signal components may be applied p to the input circuits of the actuating mechanism in accordance with a prescribed assignment or allocation to operate this mechanism from one to another of its stable operating conditions. As the mechanism is shifted between its several operating conditions, amplitude changes result and in response thereto the operating mode of the television system is likewise changed. In this manner the operating mode of the system is established for an interval introduced by each mode-determining interval and is determined by the particular code pattern of the combinap tion of code signal components in that mode-determining interval.`

At the same time, each combinationof code signal components generated at the transmitter in mode-determining intervals is radiated to subscriber receivers along withthe composite video signal. The code signal components are derived fromthe video signal at the receiver and by means of suitable filters are similarly segregated from one another for application, through a similar trans-` position mechanism, to various input circuits of a multistable actuating mechanism inexactly the same manner as at the transmitter. lfthe transposers are adjusted to the same setting, the actuator and decoder at the receiver operate in synchronism with the corresponding actuator and coder at the` transmitter to eiect intelligible image reproductionl It possible `that the multi-stable actuating mecha- States Patenti.

nisms at some of the subscriber receivers may fall out of step with the corresponding actuating mechanism at the transmitter, even though the transposition mechanisms are properly adjusted, due to overriding noise or other extraneous signal disturbances. To remedy this condition, reset pulses may be supplied to the actuating mechanism at the transmitter and at each corresponding mechanism at the various authorized receivers at the start of each mode-determining interval to restore all ofthe mechanisms to a predetermined reference operating condition for locking in or synchronizing the encoding equipment of the entire system, as described in detail in the aboveidentified copending application. With commensurate reset, or resetting at the commencement of each modedetermining interval, the actuators start olf from the same condition at the beginning of each mode-determining interval regardlessY of the condition existing at the termination of each preceding mode-determining interval; in other words, the `c ombination of code signal components occurring during each mode-determining interval is completely determinative of the operating mode assumed by the system at the termination of that interval. In accordance with the present invention, increased coding complexity is achieved by modifying the system in such a manner that the operating mode is determined not only by the combination `of code-signal components occurring during =a mode-determining interval, but also in part by the operating mode in whichlthe system nds itself at the commencement offthe. mode-determining interval. In other words, in Vsysternsconstructed in accordance with the invention, the `past history of the encoding operation is a signicant factor in determining the operating mode established by at least some of the code signal combinations; for convenience, operation in this manner is termed past history operation or past history encoding. In systems in which past history plays` an essential role in the encoding process, it is virtually impossible for an unauthorized person to examine the various code combinations and their effects on the system in an attempt to decode 0r unscramble fraudulently the coded telecast inasmuch as recurring identical code signal components cannot be correlated with any particular operating condition.

In systems of the type in which the operating mode is varied periodically or in accordance with'some iiXed or repetitive plan during the operating intervals between successive mode-determining intervals, past history operation v may be achieved with the present invention by resetting at regularly or irregularly spaced intervals recurring incommensurately with the mode-determining intervals. The

average repetition rate at which resetting is accomplished may be equal to or higher or lower than that at which mode determinations are made; so long as there are some mode-determining intervals not accompanied by a resetting operatiOn, past history operation is insured.

It is, accordingly, an object of the present invention to provide an improved encoding arrangement for a subscription television system of the general type described in the aforementioned copending application..

"It is another object of the invention to provide an encoding arrangement having enhanced secrecy aspects for rendering unauthorized decoding extremely ditiicult.

It is a further objectof the invention to provide a novel method of operating a subscription television system.

It is still another objectof the invention to provide an encoding arrangement for achieving past history encoding.

`It is an additional object of the invention to provide an improved subscription television transmitter employing past history coding.

It is a still further object of the invention to provide an improved subscription television receiver employing past history decoding.

An encoding arrangement for a subscription television system, constructed in accordance with the present invention, comprises an encoding apparatus having a plurality of operating conditions for establishing` a corresponding plurality' of'operating modes in the television system. A control mechanism is coupled to the encoding apparatus andoperates inresponse to an applied'signal forselectively actuating the encoding apparatus between its operating conditions. Means is provided for developing during a lirst mode-'determining interval a first combination of code signal components representing a predetermined rst code pattern, and' for developing during asecond andV succeeding mode-determining interval` a. second combinationof Y codesignal components representing apredeterrnined second code pattern. Finally, the encoding arrangement has means for utilizing the code signal components of the irst combination to efectactuation ofthe' controlinechanisrn thereby to establish the encoding apparatus' throughout an interval succeeding the 'rst mode-determiningdn- Y terval in one of its operating conditions determined byy the rst codepattern, and for utilizing the codev signal components of the second combination to` effect actuation ofthe control mechanismv for establishing the encoding apparatus throughout an interval succeeding both the iirst and 'second.mode-determining, intervals in one of` its operating conditions -conjointly determinedby they rst and second code patterns.

The features of this inventionvwhich are believed to be new are set 'forth with particularity in the appended claims. The'- invention, together with further. objects andv advantages thereof,'.may best be understood, however,fby referenceto the following description when taken in conjunction with the accompanying drawings, in which:

Figures 1 and 2 combined, with FigureZ being placed immediately below Figure l, constitute a schematic diagram of a subscription television transmitter constructed in the manner described in the aforementioned Bridges applica-tion; Y

Figure 3 is a family of curves useful in explaining the operation of the transmitter of Figures 1 and 2;

Figure 4 is a schematicfdiagram of a receiver for operation in conjunction with the transmitter of Figures 1 and 2;

Figure 5 is a schematic representation of a component and the manner in which it may be incorporated into the transmitter of Figures-l and 2 in order to provide a systern that is constructed inaccordance with one embodiment of the present invention;

Figure 6 is a block diagram showing a group of conrponents whichv may be'incorporated into the transmitter of Figures l and 2 or in the receiver of Figure 4 to provide Va system constructed in accordancewith another embodiment of the invention; and Y yFigures 7 and 8 show two series of waveforms helpful in explaining the operation `of the circuits shown in Figuies 5 and 6.V

The transmitter' of Figures. 1 and 2 includes a picture. converting device 10` which may be an iconoscope, image orthicon or other well-known type. The output terminals of device 10 are connected througha videoamplifier 11 and an encoding apparatus or coder 12'to the input terminals of a mixer amplilierl 131 Coder 12 may be simi lar to that disclosed and claimedin a 'copending appli-A cation of Robert Adler,.S'erial No. 243,039, ledAu'gust 22, 1951, and issuednugust 7, 1956as'PatentzJSsASs, entitled Subscription Television Systemfandfassigne'd to the present assignee. It-'may comprise a Abeam-delicoticn tube having a pair of output -circuits which may be selectively coupled into the video channelasthe electron beam thereof is deiiectedvv from one to the other of two segmental anodes coupled to such output. circuits. One of these circuits includes; a time-delaynetwork sothat the timingof thevideofcomponentsrelative jto-'the synchronizing components of the radiatedsignal-varies asthe beam of the deflection tube is switched between its anodes. This switching elect is accomplished by means of a beam-deection control or actuating signal applied to encoding apparatus 12, as explained hereinafter. Such intermittent variations in the relative timing of the video and synchronizing components effectively codes the television signal since conventional television receivers, not equipped with suitable decoding apparatus,v.depend upon an invariable time relation between the video and synchroy nizing componentsV of a received signal `to provide 1ntransmitter operation is: 'conventional''particularlyin r'espect ofthe timerelation between the video and' synchro-V nizing rcomponents of the radiated' signal. In its second operatingcondition, coder 12 introduces a timedelay in the video channel, and' the transmitterthen functions in' an abnormal m'o'de sinc'e 'th'e video' and synchronizing components of the 'radiated signal have an abnormal time relation' withl respect to one another."

Mixer amplilier 13 is connected through a direct-current inserter 14to` a carrier-wave generator and modulator 15V which, inturn, is vconnected t'o a'njantennal, 17.. The transmitter also includes a' synchronizing-signal generator. 19" whichv suppliesY lineand held-synchronizing components and associated pedestal components to mixer 13 over leadsZ: YGenerator 19 further supplies ieldand liner-drive' pulses' to a field-sweep. system 2'1and toY a line-J sweep"sy'st'em"22, respectively. The output terminalsofl sweep systems'Zl and' 22Y are connected Vto the field-decondition to' its abnormal condition in response to the trailing edge of each output pulse from multivibrator 28`to -devel'op fan output pulse of a predetermined time duration. 4The' output 'signal' from multivibrator ,29' is, in turn appliedas aA gating signal' to a normally-closed gate circuitz'.. t

.Generator19f' also supplies line-drive pulsesto a delay t,

line: 251havingoutput terminals connectedv to another input circuit ioffgate circuit v26 and further connected to an input circuit of.' another normally-closed gate circuit` 32'.,v The output terminals of 'gate circuit 26 are,

connected. directly .to a code burst generator 4.7,"through l asecond. delay line 27to anothen mono-stablemultivibrator .-31, and, overlaconductor 3`4to synchronizing-1 signalA 'generator"19." The .output terminals of multivibrator 31 :are connected to the inputte'rmi'nals. ofV gate. circuit 3 2 to establish a gating signal therefor. The

outputlsignal of circuit A32 .isA also applied to. synchronizingfsignalfgenerator 19ffover conductor 34. and iss'upplied,l Y toY a A control..` grirl;A )of a` beam-detiection 1 device.-V 382 to modulate the electron bearntherein, energizingVv or. fturningon. thefbearnffor the duration of eachapplied signal;

`Bea/rn-deliectiondevice 38; includes.` a pair 'of deflection 1 elementslp36,`3f7 whiphare connected tothe output terrnifk nalsoffanoisefgeneratorl 35. Thisgenerator produces asignalfhaving`l an-.linstantaneous'frequency that varies A in:randen-,1.,fashionI over gva suitable `bandwidth and may sweep thebeam (if it is energized)V back and forth across a family of anode segmentsr40a-40f at a rate corresponding-to the instantaneous frequency of the output signal of generator 35.

The load circuits for the several segmental anodes 40a-40f are completed through control circuits of a series of additional code burst generators 41-46, respectively. This coupling from the anode elements to the generators permits each generator to be turned on or energized by a current pulse resulting from the irnpingement of the beam in device 38 upon the associated anode segment. Each of the generators 41-47 includes a cycling or timing feature in the manner of a blocking oscillator or other mono-stable generator to determine the duration of the interval during which the generator is energized in order that the output obtained therefrom may lhave a selected duration, exceeding the current pulse delivered by its associated anode segment but less than the time separation of successive line-synchronizing pulses. Moreover, `each of the generators 41--47 has a distinct, assigned operating frequency as indicated by the indicia fl--fq to facilitate frequency selection or separation of the outputs from such generators.

The respective areas of the segmental anodes are preferably so chosen that each receives the same average current as the electron-beam is swept under the control of the signal applied to deection elements 36, 37. The

beam is thus directed to each of the anodes for an equal proportion of each program interval and has a substantially equal probability of impinging on any one of the six anodes each time the beam is gated on under the control of unit 32.

The beam-deflection device, the circuits provided for controlling the intensity and sweep of the electron beam of the device, and the generators coupled to the anode segments thereof, collectively constitute means for developing during each mode-determining interval a combination of code signal components individually having a` predetermined identifying characteristic (frequency) and collectively representing a code pattern in` accordance with their order within the. combination. Their conjoint operation in that respect will be considered in more detail hereinafter. It is convenient to utilize `frequency as the identifying characteristic of the output signals of generators 41-47 although other characteristics such as pulse width and amplitude are also suitable.

The output terminals of generators 41--47 are connected to a pair of input terminals of mixer amplifier 13 over conductors 101 and, by means of a ground connection and conductor 102, to the primary winding of a` transformer 58 which may be sectionalized, as illustrated. Means responsive to the identifying characteristics of the encoding signal components are provided for separating these components from one another. This means includes a series of secondary windings of transformer 58 which constitute the inductive portions of a corresponding series of frequency-selective tuned circuits 51-57, each suc-h circuit being resonant at a particular one of the frequencies f1-f7. The frequency-selective circuits, with the exception of circuit 57, are connected through diode rectiiiers 61--66 to a transposition mechanism 70 while frequency-selective circuit 57 is connected through a diode rectifier 67 to a reset connection 79. The transposition mechanism 70 includes a series of switching vdevices 71-76, one for each of the selector circuits 51 to 56, respectively. Each such switching device comprises a rst switch blade connected to the` anode of the diode in circuit with its selector and adjustable to engage either of two contacts. Each of these contacts, in turn, is connected to second and third switch blades individually adjustable to engage either one of a further pair of terminals so that the circuit may be extended from the input terminal of the switching device to any one of four output terminals in accordance with the adjustment of the first, second and third switch blades. r

a'saaasa The secondvand third blades of each switching device are `mechanically interconnected, as represented by the broken construction line, for unicontrolled action in respect of their contact pairs. Corresponding output terminals of the switching devices are interconnected by conductors 77a-77d. Conductors 77a-77d extend the circuits from the active output terminals of the switching devices to resistance-capacitance diode load circuits 81, 82, or 83 or, alternatively, to a ground connection 80.

The described` circuitry of transposition mechanism permits selective control of a control mechanism or multistable actuating device 103 provided for supplying a beamdeection signal to coder 12 to elect actuation thereof and coding. As shown and as will be described presently, the actuating device has two stable operating conditions resulting from the use of a pair of electron-discharge devices 77 and 78 `cross-coupled, one to the other, to be rendered conductive in alternation. If desired, a ring circuit may be used in the actuating device to provide a larger number of stable operating conditions and increase the flexibility as well as the capability of the coding technique. The use of a multi-stable actuator having a large number of stable operating conditions further reduces the number of frequency channels required for coding. Considering now more particularly the form of actuator represented, it comprises a pair of electron-discharge devices 77 and 78, the anode of device 77 being crosscoupled to the control electrode 105 of device 78 through a resistor 97 and the anode of device 78 being Vcrosscoupled to the control electrode 104 of device 77 through a resistor 98. The anodes of devices 77 and 78 are connected through resistors 96 and 99, respectively, to a source of positive unidirectional operating potential 95, and the cathodes of the devices are connected in common through the parallel combination of a resistor 94 and a capacitor 93 to a ground connection.

The control mechanism or actuator has: three input` circuits for individually controlling the conductive condition of an assigned one of the discharge paths to determine the operating condition of the actuating device.`

One input circuit, coupled to the grid 104 and cathode of tube 77 to control the conductivity thereof, comprises a diode 84 connected between the high-potential terminal of network 82 and a resistor 91. A second input circuit for controlling the conductivity of tube 78 comprises a diode 87 and a resistor 92 coupled in similar fashion in respect of the high-potential terminal of network 83 and grid 105 of tube 78. The third input circuit extends from the high-potential terminal of network 81 through one diode 85 to grid 104 of tube 77 and, alternatively, through another diode S6 to grid 105 of `tube 78. The anode of tube 78 is connected to coder 12 over conductors 100 to provide an actuating or deection-control signal therefor having amplitude variations representing a coding schedule and determined by variations in the operating condition of actuator 103.

In order to restore actuating device 103 to a reference operating condition at predetermined times,'reset connection 79 permanently connects frequency-selector 57 to the first-described input circuit of device 10.3 by way of conductor 77b.

In considering the operation of the described transmitter, the technique of coding will be disregarded initially. Picture-converting device 10 produces video-frequency components representing the program information to be t televised and these components, after amplification in am- The modulated video carrier is supplied to antenna 16, i

.17 for transmission to subscriberreceivers. It will, of

course;

to` by:V generaton 1.197: As:.in; any television .broadcastgtha accompanying audio. information .is modulated onfa; soundv im curve :3L intens-ity; modulate i the..y ,bearn,- turningn theA beam on so to speak for the duratiomofzeacmsuch pulse.-l At .':theptsamefitimegg theryariable amplitudevsweep signal t impressed; onxgdeeetion elementsigl;i 37 Y- by noise. gen;-

carrier.: and". concurrentlyeradiated. However,v the. sound system: .maya ber. entirely; conventional: and; since:,it .con-f.v stitu'tesfnofpartaoffthe: ,instant` invention; .titzha'sz not ,been

illustrated inl order' to: avoid unnecessarilyv cucumber-ing the` drawlngi..

AIt is necessary in .any commercial:..subscripdon vsystem to codethervideo signal.and preferably-.the soundsignaly aswell, to prevent. pirating .oriunauthorized use. ofthe. program material; Brieily; .coding;ofthe-.video portionY of the. broadcastis. accomplishedxby-f coder 12 under the influencer of 1 a detlectionfcontrol i signal:V which; switches.I the beam thereof `back and;forth'.betweenv itstwo segmental anodes in accordance with a'coding schedule. represented by amplitude variations ofthatsignal. As previously explained, this actuationof the coder varies the operatingmode of the: transmitter, modiiies the time relation of` the video and. synchronizing: components of the. radiated signal, and achieves'coding. Consideration will now be given to the particulartmannerfin which. the telecast is coded.

Periodically recurring .line-.drive. pulses, shownin curve 3A, are suppliedfromgenerator 19to delay line 25 to establish the pulses .of .curve 3B.v This: line isterminated in its .characteristic 'impedance and; exhibits a delay exceedingfthe duration of theline-,drive pulses but substan tially lesslhan ,theztime separation .ofzsuchpulsesv Simultaneously with the application-of:linedrive pulses to delayV line 2S;.periodically recurring` field-,drive pulses, shown in curve 3C, are applied to. multivibrator 28. Theleading edge of an appliedfieldfdrivepulse actuates the multivibratorfrom its normal: operatingvconditionto an abnormal. operating condition and the multivibrator automatically returnsto .itsnormalcondition after a selected time interval determined by itsinternal cycling circuits to produce the pulse of curvev 3D: The parameters ofthe multivibrator are so chosen that the trailing edge of this pulse occurs during the field-retrace time. of the system, at a point. following the equalizing. pulses which succeed the serrated iield pulse in present-day practice. This output signal is applied to mono-stable multivibrator 29 which responds to theY trailing, edge thereof and produces a gatingy pulse, shown in curve 3E. The parameters of multivibrator 29 are so chosen that this pulse overlaps, in point of time, one pulse. from: delayv line 25. Gate circuit 26 receives the gating pulse as well asv delayed line-drive pulses from delay line 25 and responds to their coincident effect to translate a pulse. (curve 3F) to generator 47. rlfhis generator isY energized by the applied pulse and develops aV burst of signal of frequency fr, having a time duration exceeding the duration of the actuatingpulse, but less than the time separation of successive line-synchronizing` pulses. This signal burst of frequency fr, produced at the outputterminals of unit 47 is for reset purposes and isy shownin `curve 3J. The utility of this reset burst will be shown hereinafter..

Thefoutput signal from gate circuit 26- (curve 3F) is also delayed in delay line 27 which isV terminated in its characteristic impedance and which exhibits such a delay that its outputl pulse, shown in curve'SG, follows the trailing edge of the pulse of curve 3F. The delayedout put pulse is applied to mono-stable multivibrator 31, producinga gating pulse, shown in curve 3H for gate' circuit 32.. The parameters.ofqmultivibratori 3'1 are so chosen that its output pulse (curve 3H) overlaps, in point of time, the number of. delayed line-drivepulses.,(curve 3B) to be employed in coding-siicfoi thet'case.. in: question.. Delayedline-drive pulsesare continuously supplied. from; delay line 25 to gate circuiti-32y and' those which occur within; the; duration; of thecgatingpulse. are translated to. beam-dellection device 38. The translated pulses, shown a vburstof signa-L.. of frequency f3.

assumed that` as Pthe. succeedingvpulsesof curve 31 occur,

erator `35..creates^.a; deection..field var-yingrzat `a random. rate tosscanffthe'pbeam;back andfforth'r across segmental. anodesf.iizz--elt ,Each..;time2 apulse. of Vcurvepl is applied .-to thecontrol-.electrode la pulse of current'iiowsini the circuit ofionefof the segmentahanodes. tof-turn on the: one of generators11g-46that-iscoupledA thereto. In the presentillustration,z fon exampleg it will'zbeassumed thatzwhenythe. firstA pulse of-curve` 31 ocursf, the beam-.

is -directedftoanodetik:y and y, thus generator i3 produces* generatorsfdZnl, ,41,..44;,and42, are. turned on in the. recited.orderfproducingcorresponding. bursts of signal of 'frequencies fh fm. f1, Jf4,.,and.f2,` as Yshown in curve.

3]. A combination of .code signal componentsofvarious t frequencies; is thus. established, the. components, being randomly-sequencedand.'.randomlyfappearing within their combination.,

These..codesignal. components, are impressed on the primaryfwi'nding ,of transformer 58., and are. selected by means ofifrequency-selectors1512-57. Inother words, the rstburst ofjsi'gnal"offfrequency f7 is segregated'by selector,57l,"t`lie secondburstofls'ignal of frequency f3 is segregated' byfs'eliector.53,'I the third burst of signal of. frequencyjfzv Iis ychosen by selector 52;'and soon, Assuming that transposition mechanism 7i) is adjusted as illustrated selector 51 is coupled through' diode 61 and" to` load circuitf?Y andi selector 55 is .coupled to load". circuit Si, L'Thus, the, reset' pulse shown. in. curve Klis;V developed irrinetworli'SZin'response to the burst of 'psig-f nal frequency f7; the'V pulses; of v.cur-ve' li are develop'edin network .81; in` response tojthe` two" bursts of signal freiV quency fgandt'h'e single: burst ofl signalA frequency f6; andthe pulses shown in'curve Mf'are. developed in net- Work' 33Cinresponse tothe burstof'signal frequency f3 It willbe noted andl theY burst of; signal' frequency f1'. that the burst'of si'gnallf'requencyf.,A is channeled directly to the Vground andL develops no signal potential in the load circuits; Y

'It is'thus seen''thatjthetranspositionr mechanism receives a-Yparticularcombination-off code signal components (curve 3i) andit'ransposesithat combination into a different etfective combination (curves'K, L` and Mv) deter-- minedz'bry-I tlieadjustmemnt ofitsswitch elements 71 to 756: which directthe pulses of-Qthey first combination iny respect of the* input `circuits of-tlie control mechanism or `loi-stable actuatingdevice 103. In considering the transpositionf-el'ectedf by-.niechanism 70 it willbe manife'st that-the distributionf ofthe coding pulses in respect of the input'- circuitsof actuating device 103V is Yparticularly signilicant in determining the final coding pattern.. The specic setting of transposition mechanism- 70Y may be clian'ged'a't willl although `it"is"convenient to adjust the;y meohanismaatlthe start.' of a program andmaintain it throughout thel program.. The switch setting informationy is.:dis'seminatedf'onlyt'o-` subscriber receivers and av suitable: charge: may/,of course, be assessed for. such infomation.

Cor'isider` that in :gthe lrst orv reference operating condi- Y.

tionwof 'actuator 103;,tubef77'ris non-conductiveandtube 78is highlytconductive;,further consider that in the sec ond or; alternativeoperatinggcondition, tubeA 77 ishighly conduct-ive; and'tube 73.is noneconductive.

the start of the mode-determining interval. The resetV It will' further.V beC pulse of curve 3K `which is received first is applied to control electrode 104 of device 77. Thereset pulse biases device 77 to cut-off and the cross-coupling causes device 78 to be conductive, thus establishing the reference operating condition in the actuator. If actuating device 103 is in its reference condition at that time the reset pulse has no effect at all. is certain to be in its reference condition at the beginning of each combination of coding signal pulses; the period for the combination is called a mode-determining interval inasmuch as the combinationrdetermines the particular mode of operation of the system for an ensuing operating interval, i. e., the succeeding field-trace interval in the particular illustration;

The next pulse, which is the rst component of curve 3M, is applied from network 83 to control electrode 105` and causes device 78 to be driven beyond cut-off which, in turn, renders device 77 conductive. The actuator is thus triggered to its second operating condition. The next succeeding pulse of the coding combination which is the first pulse of curve 3L is impressed simultaneously on both control electrodes 104 and 105 from network 81. Device 78 being already non-conductive is not effected by the negative signal on its control electrode 105, whereas device 77 being in its conductive state is rendered non-conductive and device 78 then becomes conductive. The next succeeding pulse `of the coding combinationywhich is the second component of curve 3L, is also applied from network 81 to control electrodes 104 and 105. The negative signal applied to control electrode 104 has no effect on device 77 whereas the signal impressedon control electrode 105 biases device 78 beyond cutoff which renders device 77 conductive. The actuator thus assumes its second operating condition. The next pulse of the transposed combination, which is the second component of the curve 3M, is applied from network 83 to control electrode 105 but has no effect `since device '78 is already non-conductive. The next pulse of the original combination, a burst of signal offrequency f4, is applied to ground through switch element 74 and does not reach actuator 103. The final pulse of the transposed combination is the last component of curve 3L and is applied from network 81 to control electrodes 104 and 105. It triggers the circuit to its first operating condition.

The resulting signal obtained from device 78 of bistable actuating device 103 (curve 3N) is applied to coder 12 over conductors 100 as a deflection-control sigi nal. The amplitude excursions of this signal shift the beam of coder 12, and the amplitude level of the signal at the conclusion of the response of actuator 103 to the transposed code combination determines the operating mode of the system until the next succeeding mode-deter mining interval at which time the aforedescribed modedetermining process is repeated. In view of the random manner in which the frequency components may appear in"` `the `original combination (curve 3J), it is apparent that*themode-determining process causes the operating modeof the system to change from time to time in accordance with a random coding schedule. As a consequence, the transmission is coded.

In order that subscriber receivers may utilize the coded transmission, it is necessary that the combination of code signal components developed by beam-deflection device 38 and its associated circuitry be made known to such subscriber receivers. bination (curve 3J) is applied to mixer amplifier 13 at the same time it is deliveredto transposer 70 to be cornbined with the composite video signal for transmission to subscriber receivers. The bursts of various signal frequencies, which constitute the code signal, occur between the line-drive pulses superimposed on the vertical-blankV ing pulse, and therefore it is desirable that the amplitude level of the blanking pulse be modified to effect an inward modulation of theblanking pulse by the coding signal In this manner, the actuator components. To that end, the pulses shown in curves 3F and 3l are supplied to synchronizing-signal generator 19 over conductors 34 to produce suitable modulating pulses which, in turn, are supplied to mixer amplifier 13l over conductors 20 to downward modulate the vertical blanking pulse at the appropriate times. inasmuch as the time duration ofthe modulating pulses should equal the duration of the signal bursts (curve 3J) and will therefore exceed the duration of the actuating pulses shown in curves 3I and 3F,' signal generator 19` may include a timing device, such` as amono-stable multivibrator, to develop such modulating pulses of selected time duration in response `to the `actuating pulses. The effect of the application of these modulating pulses and the code signal components to the `mixer amplifier 13 is readily apparent` by observing the wave' form of the radiated composite video signal shown in curve O.

It should be mentioned at this time that in the particular illustration the codersignal componentsare produced during a portion of the vertical-retrace interval so that `mode changes will be `effected between field-trace intervals. However,iit` "should be understood that the code signal may be developed and utilized at other times, for example during `line-retrace intervals, if so desired.

The receiver ofFigure 4, which may utilize the telecast Aoriginating atthe transmitter of Figures l and 2, com` prises a radio-frequency amplifier 110 having input terminals connected'to an antenna circuit 111, 112 and output terminals connected to a first detector 113, the output terminals of the detector being connected to an intermediate-frequency amplifier 114. The output terminals similar to coder 112 at the transmitter except that `it is*v controlled to operate in a complementary fashion in order t effectively to compensate for the variations in the timing of the received television signal.

Second detector 115 is also coupled through a synchronizing-signal separator 122 to a field-sweep system 123 and a line-sweep system 124. The output terminals of sweep systems 123 and 124 are connected respectively to field-deflection elements 120 and line-deflection elements 119, associated with reproducing device'121. f

To that end, the code signal com- Field-drive pulses derived from synchronizing-signal:

separator 122 are supplied to a mono-stable multivibrator 125 having output terminals connected to a normallyclosed gated amplifier 126. The output terminals of second detector 115 are ralso connected to gated amplifier 126 to supply the composite video signal thereto, and the output circuit of this amplifier is completed. through a sectionalized primary winding of a transformer 138 to a source of unidirectional operating potential 127. A series of secondary windings of the transformer constitute the inductive portions of a series of frequency-selective tuned circuits 131-137, individually resonant at a particular one. of the seven frequencies employed in coding. Selectors 131 to 136 are connected via associated diode rectifiers141-146 to a seriesof switching elements 151-156 while selector 137 is directly connected via a reset connection 182 to a parallel resistancecapacitance load circuit 161.`

or to ground.

Load circuit is connected via conductor 184 and a pair of isolating diodes 165, 164.to the control elec- 1 trodes 178 and 179 of a pair of electron-dischargey devices': 171 and 172, respectively, of an actuator 183. '.These.

control electrodes are connected to ground through re* sisters 167 and 168, respectively. Load circuits 161 and Switchingf elements 151v 156 constitute a'transposition mechanism 158, similar to. mechanism 70 of the transmitter, provided to connect` any one of the selectors 131-136 to any one of three` parallel resistance-capacitance load circuits 160, 161, 162

172 through a resistor175 and the anode of device 172y is cross-coupled to thecontrol electrode-,17S of'devicey 171 through a resistor 176. The anodes ofdevices 171,V 172 are also connected4 throughresistorsfV 173; and174,x,

respectively,rto a source ofV unidirectionalifoperating potential 177 and the cathodes lof thefdevices are connected in common through the parallel combination of a resistor 170 and a capacitor 169 to aground connection. The anode of device 172 is connected tol decoder 117 over conductors 181 to provide nan actuating or deflectioncontrol signal therefor. The decoding arrangement snowri in Figure 4, comprising the frequency-selective circuits, the transposition mechanism; andl the bi-stable actuating circuit is identical to the corresponding arrangement shown in Figure 2.

In operation, thev coded television signal from the transmitterof Figures;.1 and 2 is intercepted by antennay circuit 111, 112, amplified by radio-frequency amplifier 110 and heterodyned to the selected intermediate-frev quency of thereceiver-in first detector 113: The resulting intermediate-frequency signal is amplified in intermediate-frequency amplifier 114 and detected in secondv detector 115 vtoproduce a composite; video signal. T his latter signal is amplified in video amplifierl 116 and impressed on the input electrodes 118 of. image reproducing,`

device 121 through decoderl117 to control theY intensity of the cathode-ray` beam of the device in well' known manner.

The synchronizing components are separated inseparator 122, the field-synchronizing components beingv utilized to synchronize sweep system 123 and, hence, the field scansionof image-reproducing device 121, Whereas the line-synchronizing components are utilized to, synchroni'ze sweep system 124 and, therefore, the linescansion of device 121. Of course, the sound modulated carrier received along with the video carrier is translated in the usual way through an audio system which has been o-mitted from the drawings for purposes of simplicity.

Field-drive pulses from separator 122 are supplied'to mono-stable multivibrator 125 to'produce a gating pulseV shown in curve 3P lfornorrnally-closed gated amplifier 126. The parameters of the multivibrator areso chosen as to overlap, in point of time, that portion of the fieldretrace interval of the composite video signal (curve 30). which includes the resetpulse and the other encoding signal. pulses. The composite video signal is continuously applied to the, input circuit of amplifier 126 butonly the information. contained during the interval of the gating pulse. (curve 3P)Y is translated to the primary winding of transformer .138., Amplifier 126 is thus open during the times the signal bursts of various frequencies, representing the combination of code signal pulses, are received and consequently such bursts are separated out by the selector circuits 131-137 in the same manner as in the transmitter. When the various switching elements 151- 1-56 of transposition mechanism 158 are adjusted to the same setting as transposition mechanism .70 at the transmitter, the input circuits ofA bi-stable actuating device 183 receivey the identical pulses received by the corresponding input circuits of bi-stable actuating device 103 of the transmitter to produce an actuating or deflectioncontrol signal for decoder 117 identical in wave form to curve 3N. Decoder 117 therefore operates in time coincidence with coder 12 at the transmitter yso that the signal applied to electrodesy 118 of image-reproducing device 1-21 is suitablyfcompensated to effect proper image intelligibility.

The-entire systemo Figures 1 4'. is reset to thesame predetermined reference conditionin preparation. for each combination of code signal components. Consequently,

f rinsfzduring.- that interval.

tiiegniode;v established at-,the'terniination of each inode; determining interval is determined solely by the nerf.

tieularcombnation of codesignal.;Components .occur-` accordancezwiththe present,invention. the past history oftheencoding apparatus playsy an Vessential role infthe rnodegdeterminingoperation; in other words, eachy specific, combination ofr code signal components may effectuate different mode-determinations at different times, depend-l ing on the operating conditionof the encoding apparatusV atthegcornmencement of the mode-determining interval. Ina system employing a randomvariation of the code,

signal combinations from one mode-determining.interval1 tothe next. the operating mode at the, commencement of a1given mode-determining interval is dependentgupon the. previous codesignal combination and its mode dev-YA termination. Thus, the operating mode established at the,A termina-tion of. the mode-determining interval is` deter.-

minedconjointly by the code signal combination appearf.

ing. within that interval andthe combination of code signal components occurring within a previous modef, determining interval.

To accomplishfpast history. operation of thev system Ain` accordance with theinvention, the `transmitter of Figures l and 2 may bemodified to provideJ resetting ofil controlmechanism 103 at the transmitterfand correspond ing control mechanism 1783 at the receiver at intervals re curiing.incommensurately with the mode-determining intervals. This may be Vachieved by interposing a randomfrequency divider 187 between gate circuit 26on the.`

onefhand and f7 generator 47 and conductor- 34 on-the other,in the manner indicated by substituting FigureA 5 for the portion of Figure 1 designated in dashed outlirie- This random frequency divider may be constructedl in the manner described in Patent 2,588,413, issued March 11, i952, to Erwin M. Roschke, and assignedi to the present assignee, such that the applied input pulsescombinationsoccurringin different and successive mode-r determining intervalsindicated A-F, specificallygsucces-v sivev field-retrace intervals, have been added. It will beV seen that inasmuch as only certain ones of the pulses ofl curve F" are -effectively translated by'random frequency divider 137, reset burstsof frequency y", occur onlyv at" the beginningof mode-determining intervals A, D, and FiA As explained hereinbefore', the pulses of,` curve J" are separatedand, after-rectification, are applied tothe vari# ousinput circuits v of actuatorss103;and"183A to` produce identically shaped signals for effectingactuation of coder 121 and decoder-i117. In accordance with the illustrative switch setting r ofl the transposition-rnechanisms shownk in Figures 2 andn 4, the signa-l1burstsoflcurve Vare applied v i to the var-ious inputcircuits of 'the' Acontrol, mechanisms 1031 and'liin such a manner that the signalV shown in. 'i

curve-Nein Figure 7 (redrawn-f'rorn curve N) is rpro.- duced 1n eaclr meclianismsfor'l application to its associatedencoding.apparatus.- Y i' Y f i v Examination .off-curve-N' revealsf-*the beneficial vresults Y achieved: Ybylernpliiying .reset pulses that-.occur incommensurately with.` the mode-determining intervalsgforvexjample, resetpulses Ythat appear less frequently than thc-V mode-determiningl interval; During I a mode-determining 1nter.valinA which 'no-reset pulse is present, the operating;` modelof-Z theisystem: forftheperiodinimediately succeeding that I modedeter-rnininginterval is determiried'- not onlyiby j the? code-.pattermof the combination-of code'v components occurring during that interval but also in part by the code Iny systems constructedin` :pattern of the combination appearing A duringy the precedfing mode-determining interval.`

.in .the system; is not already estabnshed in its reference operating, mode atthe commencement of a mode-detervv mining interval in which no f7. reset lburst isV present, the

code combination occurring during that interval may re- ,sult in theestablishmentof the same or ajditlerent operating.mode.than,in` 4the case'where a resetburst is present. To`.illustrate,` the code,components'ofcurve J ocgcurring' during,,molde-determining intervalC have been shown, along 'with an f7 reset burst, as curve' U in Figure 8. Assume;that each control mechanism '103,' l183 is established in its non-referenceoperating Vcortditionbefore the arrival :of the signal `burstsfof curveiU,l as indicated by the relatively positive potential level-of curve V which would appear at the same point in each actuating circuit as curves N and N."E`ach.control mecha- .nisrn is. actuated in response to 'thejfqreset.pulsetoits ,reference operatingcondition sothat thejsignal of curve `V undergoes a negative excursion` as' shown.,j"S1nce the., vsucceeding pulses occurring in modedetermming interval C (namely f2, f6, f2, f6. te, f2) are applied to the input Cr- `.determining interval C in the condition wherein the outputsignal is established at its negative potentiallevel.

Assume now that the fr, reset,b urs't` is ,not present 1n the. combination illustrated in curve U, ibut-.assume fur-` ,ther `that .each control 4mechanism is already. .established in itsreference operating condition as shown by, the relatively negative potential level at the L begmr'ung of curve QW `which represents the outputA signal ,of fthe, multivi- `brators. `In this case, the presencerorabsence;of Ya reset ,pulseds of `no consequence inasmuch as ,eachcontrol mechanism is already establishedin itsY reference condition. The control mechanisms are therefore actuated `from `the `reference condition in,responseto'thebursts fz, fa, zyfe, fs, f2, t assume the sameoperating condition t at thetermination of interval CA as in the casepreviously described in` connection with curvey V. `This can very easily be -seen by comparing curvesWand V.

. However, if the f7 reset pulse is not presentm theicode signal combination of curve .U .and ifthe.. actuators are established in their non-reference .conditionat the commencement of the mode-determining interval as? shown by the relatively positive potential `of..curve X which rep- `resents` the signal appearingat .the outputfterminalsfof ,control mechanisms 103 and.183 theirsttburst` (f2) triggers each multivibrator to itsreference conditionandathe subsequent bursts (f6, f2, fw f6, f2),.eiect,actuationfback and forth, the'multivibrators,winding up1at..the..termina V`tion of mode-determining interval C.inthe.condition .in `which the loutput `signal of curveX is. established at` its .positive potential level rathextthantthe` negative level.

..Infother words, the `effect of thepar-ticularscode l. signal A,combination on the encoding :operation is 'dependentupon the operating mode of thegsystern,at-.thecommencement `ofthe mode-determining interval in :which the ,codetsig- .i nal combination occurs.

In the foregoing discussion of the electqofzornittingthe f7 reset burst, it has been convenienttofconsidertaaparticular code signal combination composedentirely of coming mechanism.

,ponents directed, through the rect-ifers :and .the `transpofsition switch, to; the common inputcircuit ofthefencoderi iactuating mechanism, so that eachzcodefsignal burst re- `sults in a change in the operating 4condition of the actuat- In actual practice,` however, Athe code signal bursts .are randomly distributed in each combinanecessarily, result in ,a change in the operating condition at. atime when no. such; change. wouldt-.be-eected-wth A Ycomr'nensurate reset or'vice versa.

j Thus, in the-absenceof a resetpulse precedingfthe com-1 ,birration of code signal,componentsrduringgany one par-l 'ticular mode-determining` interval,`j'the pastghistory of the system has a'very delinite-andposiftive `effect onthe op-4 eration. *An interdependence betweenthe'various combinationsof code signal components is `present so that similar combinations may render different results. K This feature further increases the .codingcomplexity and makes it virtually impossible for-an unauthorized person to examine various code signal combinations and their respective-eiects on the operationfof Athetelevision system and 4arrive" at the correctycoding schedule by ordinary methl5`` ods" ofA cryptographic analysis.

`-As a furtherwariant oft'theinventiom Figure 6illusytrates circuitry that'may-be introduced into the receiver `of Figure 4` aswell asthe transmitteriofFigures 1 and 2 in order to additionally enhance'thesecurity aspects of -the televisionl system.l Briey,in thisembodiment the reset pulses notfonly` occur less frequently than the modedetermining intervals nbut,A arefurthercoded so that only l authorized receiversknow exactly which reset pulses are to be used. rThisisV achievedin the-embodiment of Figure 6 by disconnecting. point`80' at the transmitter `from theground connection andinsteadconnecting this point to a rectifier load .cirouit^188.` Sincethe switchesof'the transposition mechanism aresoadjustedthat the f4 tuned circuit is connected to point 80 atthe transmitter, the @bursts will `be chann'elled-to-lload circuit 188. This `load circuit is connectedto-the input-terminals of a monostable multivibrator189.

Consequently, each time aany f4 burstvoccurs in any of :the variouscode signal combinations -and is selected by :means of tuned circuit154v at theitransmitterras shown in `curve S,*multivibrator1'89 is'triggered from its normal to its abnormal operating .condi-tion. The parameters 4of multivibrator1189 `areso chosen that Vthe output pulses,

pulse from load circuit1188, have a duration exceeding a ,field-trace', interval-andi always overlap. in i pointv of `.time

-the position in which the: f7 reset burst occurs, if it does iappear in the mode-determining` interval immediately suclceeding the interval exhibiting the f4burst.

The output terminals of multivibrator189are connected .to onefpair of input terminals1of a? normally-closed gate circuit in order toprovide a` gating signal therefor, thisgate having another pair of input-,terminals connected totheanode of diode `6.7 `and. ground. The output termi nals of normally-closedgate circuit 190. are connectedto ground and resetconnection"79.

The `circuitry of Figure 6V may.also be :included in the :receiver ofvFigure 4 merelyfby disconnectingupoint 186 from ground and,` connecting it to load circuit 188,` disconnecting the anode of diode 147 `from reset connection 182 and connectingrthat` `anodeto one input circuit of gate circuit 190, andalsobyconnecting -the output-circuit of gatecircuit :190 to reset connection Y182. The manner of operation .off theelements shown in Figure 6 is identical in transmitter and receiver.

With this arrangement, each f7 reset pulse. is supplied to gate circuit-190` and,` depending Ionthe `condition of multivibrator189, `is either used or rendered ineffective.

, If` an f4 pulse appears in 'the mode-determining interval preceding that inwhich the f7 resetipulse appears, a' gating signal is applied to gate circuit 190 to permit that f7 pulse `to reset the control mechanism. `On the other hand; if

an f4 pulse is not present in the preceding combination, the f7 burst is not gated in or translated to the control mechanism.

Curve N' has been redrawn as N" in Figure 7 to show the eiect of disregarding certain reset pulses in accordance with a coding `schedule-known only to authorized subscribers. That is, unless a subscriber-knows that the f4 `bursts-are `to, be used to gate-,intanyv subsequent f7 l resety pulses, decoding is not possible. By examining curve N" it will .be seen thatonly the f7 pulses that occur in time coincidence with a gating pulse of curve T are effective. Conversely, the reset pulse occurring at times not coincident with a gating pulse are ineffective. The difference in operation of the system when adapted in the manner shown in Figure 6 (curve N) as compared to that previously described in connection with Figure (curve N') is readily apparent when the 'system is con- 'sidered during, for example, mode-determining interval D. In that interval reset .pulse f7 is not `used in the Figure 6 embodiment since no f4 burst occurs in modedetermining interval C and consequently at the termination of mode-determining interval D the output signal from the control mechanism is established at its positive level (curve N) whereas in the case of Figure 5 where f7 burst is effective the output signal of the control mechanism is established at its negative level (curve N).

With gated incommensurate reset in themanner described in connection with Figure 6, it is also possible to transmit reset pulses. at the commencement of each modedetermining interval; in addition to permitting a simplification in transmitter equipment through'the omission of random frequency divider 187, this type 'ofV operation renders the code schedule even less susceptible tounauthorized appropriation by imparting to the transmitted signal the appearance of ione resulting from the use of commensurate reset. f

The invention provides, therefore, a subscription television system in which increased security is yachieved by virtue of the partial dependence of the encodingioperation on the past history of the system. f

Certain features described in the presentapplication are disclosed and claimed in one or more of the following copending applications: Serial No. 35,698, filed June 28, 1948, in the name of Erwin M. R-oschke et al.,'!and issued October 20, 1953, asPatent 2,656,405; Serial No'. 36,778, filed July 2, 1948, in the name of Richard O. Gray et al., and issued October 20, 1953, as Patent 2,656,406;V Serial No. 94,643, filed May 21, 1949, in the name of Richard O. Gray et al., and issued October 20, 1953, asY Patent 2,656,408; Serial No. 138,232, filed 'January -l2, 1 950, in the name of George-V. Morris et al., and issued Oct-ober 20,. 1953, as Patent 2,656,409; Serial No. 245,178; filed September 5, 1951, in the name of George V. Morris etal., and issued October, 20, `1953, as-Patent 2,656,411 Serial No. 281,418, filed April 9,1952, inthe name of George V. Morris; Serial No. 291,714, filed June 4, 1952, in the name Lof Carl G. Eilers et al.; Serial No. 310,309, filed September 18, 1952, in the name ofAleXander Ellett; Serial No. 366,727, filed VJuly 8, 1953, in the name of Erwin M. Roschke; and Serial No. 370,174, filed July 24,A 1953,v in the name ofy Walter S. Druz, all of vwhich are assigned to the present assignee.

While particular embodiments of the inventionhave been shown .and described, modifications may be nade, and it is intended inthe appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

Iclaim: Y l Y I i l. An encoding arrangement for a subscription. television system comprising: encoding :apparatus having a plurality of operating conditions 'for establishing a' corresponding plurality of operating modes in said television system; a control mechanism coupled to said encoding apparatus and yresponsive tojan' applied signal for selectively actuating saidxencoding apparatus between its aforesaid operatingl conditions; means for-'developing during a first mode-determining interval a first combination of code signal components'representing a predetermined first code pattern andf'duringva second andsucceeding modedetermining interval'a secnd combination ofcodesignal ponents of said first combination'to effect actuation of said control mechanism therebyY to, establish said Vencoding apparatus throughout an interval succeeding Said rst v mode-determining interval in one of its -operating conditions determinedby said first code pattern, and for utilizing said code 'signal c'omponents of said second combination to effect actuation of said control mechanism for establishing said encoding apparatus throughout an interval suci vision systemfcomprisingi encoding apparatus havingk a plurality of operating conditions for establishing aY correspondingplurality of operating `modes in said television system; acontrol mechanism coupled to said encoding apparatus andresponsive ,to an applied signal for selectively actuating said encoding apparatus between its aforesaid operating conditions; means for` developing during a frst'mode-determinin'g Vinterval a first combination of codefsignal components individually having a predetermined videntifying characteristic and collectively representing'fa predetermined first code pattern in accordance with their distributionwithin said first combination, and for developing during a second and succeeding modedetermining interval a second combination of code signal components Aindividually having a predetermined identifying characteristic and' collectively representing a predetermined second' codeV pattern in accordance with their distribution within said'second combination; and means for utilizing said code signal components of said first combination to effect actuation of said control mechy anism thereby to` establisli said encoding apparatus throughout an interval, succeeding ,said first mode-determiningintervalin'one yof'fits operating conditions determined by said first code pattern, and for utilizingrsaid code signal componentsof saidA secondrcombination to effect actuation ofY said ,control mechanism forestablishing said encoding apparatus throughoutan'interval succeeding both saidfirst and second mode-determining intervals in one of'its operating conditions conjointlyrdetermined by said first afnd'second code patterns.

3. An encodingarrangement for a subscription television system comprising; encoding apparatus Vhaving a plurality of operating conditions for establishing a corresponding plurality of Voperating modes inV said television system; a multi-stable control Ymechanism coupled to said encoding apparatus having a plurality of operating conditions, at least some of whfichare effective to establish said encoding apparatus in assigned ones of its aforesaid operating conditions; atleast three input circuits included in said control mechanism Aand individually responsiveto an actuatingsignal to operate said control mechani'smfrom one to another of its aforesaid operating conditions; means for developing during a first mode-determininginterval a first combination of code rsignal components individually having a predeterminedr identifying characteristic and collectively representing a predetermined first-code pattern in accordance with their order Vwithin said first combination, and for developing during a second and succeeding mode-determining interval a second combination of code signal components individually having a predetermined identifying characteristic and 'collectively representing a predetermined second code' pattern in accordance with their order within said, second combination; and means coupled to said last-mentioned means and to saidV input circomponents representing a predetermined second code.

pattern; and means for utilizing said code signal comcuits for utilizing said-code signal components Vofsaid first combination to apply actuating signals to said input circuits for effecting actuation of said control ,mechanism to establish said encoding apparatus` throughout an interval succeeding said first mode-determining interval in one of its operating conditions determined by said first code pattern, and for utilizing said code signal cornponents of said second combination to apply actuating i signals to said input circuits for effecting actuation of said control mechanism to establish said encoding apparatus throughout an interval succeeding both said rst and second mode-determining intervals in one of its operating conditions conjointly determined by said iirst and second code patterns.

4. An encoding arrangement for a subscription television system comprising: encoding apparatus having a plurality of operating conditions for establishing a corresponding plurality of operating modes in said television system; a multi-stable actuating mechanism for said encoding apparatus having at least two stable operating conditions and effectively including a plurality of electron-discharge paths cross-coupled, one to another, to render said paths conductive one at a` time in a controlled sequence; at least three input circuits included in said actuating mechanism and individually responsive to an applied actuating signal for controlling the conductivity condition of' an assigned one of said discharge paths to determine the operating condition of said actuating mechanism; means for developing during a iirst modedetermining interval a first combination of code signal components individually having a predetermined identifying frequency characteristic and collectively representing a predetermined rst code pattern in accordance with their order withinsaid first combination, and for developing `during a second and succeeding mode-determining interval a second combination of code signal components individually having a predetermined identitying frequency characteristic and collectively representing a predetermined second code pattern in accordance with their order within said second combination; and means coupled to said last-mentioned means and to said input circuits for utilizing said code signal components of said rstl combination in a prescribed sequence to apply actuating signals to'said input circuits for effecting actuation of said -actuating mechanism thereby to establish said encoding apparatus throughout an interval succeeding said? rst mode-determining interval in one of its operating conditions determined by said first codepattern, and for utilizing said code signal components ofv said second combination to apply actuating signals to said input circuitsfor effecting actuation of'said actuating mechanism for establishing said encoding apparatus throughout an interval succeeding both said rst and t second mode-determining intervals in one of its operating conditions conjointly determined by said first and second code patterns.

5. ln a subscription television system for translating a television signal including video-signal components in recurring trace intervals and synchronizing-signal components in intervening retrace intervals: encoding apparatus having a` plurality of operating'conditions for establishing a corresponding plurality of operating modes in said television sys-tem; a control mechanism coupled to said encoding apparatus and responsive to an applied signal for selectively actuating said encoding apparatusV between its aforesaid operating conditions; means for developing during a lirst` one of said retrace intervals a first combination of code signal components representing a predetermined iirst code pattern and during a `second and succeeding one of said retrace intervals a second combination of code signal components representing a predetermined second code pattern; and means for utilizing said code signal components of said first combination to effect actuation of said control mechanism thereby to establish said encoding apparatus throughout at least a portion of atrace interval succeeding said rst retrace interval in onei of its operating conditions determined by said rst code pattern, and for utilizing said code signal components of said secondcombination to effect actuation of said control mechanism for` establishing said encodingA apparatus throughout at least a portion of a trace interval succeeding both saidy first and second retrace intervals in one of its operating condiasaaaes tions conjointly determined by said iirst and second code patterns.

6. In a `subscription television system for translating a television signal including video-signal components in recurring field-trace intervals and synchronizing-signal components in intervening eld-retrace intervals: encoding apparatus having a plurality of operating conditions for establishing a corresponding plurality of operating modes in said television system; a control mechanism coupled to said encoding apparatus and responsive to an applied signal for selectively actuating said encoding apparatus between its aforesaidoperating conditions; means for developing during a first one of said field-retrace intervals a first combination of code signal components representing a predetermined first code pattern and during a second and succeeding iield-retrace interval a second combination of code4 signal components representing a predetermined second code pattern;` and means for utilizing said code signal components of said rst combination l to eiect actuation of said control mechanism thereby to bination to effect actuation of said control mechanism` for establishing said encoding apparatus throughout at least a portion of a field-trace interval immediately succeeding said second field-retrace interval in one of its operating conditions conjointly determined by said first and second code patterns.

7'. ln a subscription television system for translating a television signal including video-signal components in recurring field-trace intervals and synchronizing-signal components in intervening field-retrace intervals: encoding apparatus having a plurality of operating conditions for establishing a corresponding` plurality of operating modes in said television system; a multi-stable actuating. mechanism for said encoding apparatus having at least two stable operating conditions and effectively including a plurality of electron-discharge paths cross-coupled, one to another, to render said paths conductive one at a time in a controlled sequence; at least three input circuits included in said actuating mechanism and individually responsive to an applied actuating signal tor controllingV the conductivity condition of an assigned one of said discharge paths to determine the operating condition of said actuating mechanism; means for developing during a rst one of said field-retrace intervals a first combination of code signal components individually having a predetermined identifying frequency characteristic and collectively representing a predetermined lirst code pattern in accordance with their order within said iirst combinatiom and for developing during a second and succeeding one of said field-retrace intervals a second combination of code signal components individually having a predetermined identifyi ing frequency characteristic and collectivelly representing a predetermined second code pattern in accordance with their order Within said second combination; and means coupled to said last-mentioned means and. to said input `circuits for utilizing said' code signal components of said rst combination in a prescribed sequence to apply f actuating signals to saidY input circuits for effecting actuation of said actuating mechanism therebyk to establish said encoding apparatus throughout a field-trace` interval immediatelysucceeding saidiirst field-retrace interval inone of its operating conditions determined by said iirst code pattern; and for utilizing` said code signal componentsn of said second combination in a prescribed sequence to apply actuating signals to said` input circuits for effecting actuation of said actuating mechanism for' establishing said. encoding apparatus throughout a` iieldftrace interval immediately succeeding said secondt eld-retrace interval in one of its operating conditions conjointly determined by said rst and second code patterns.

l V8. A coding arrangement for a subscription television transmitter comprising: coding apparatus having a plurality of Vrojgierating conditions for establishing a Vcorresponding plurality of' operating modes in said television transmitter; a control mechanism coupled to said coding apparatus and responsive to an applied signal for selectively actuating said coding apparatus between its aforesaid operating conditions; means for developing during a first mode-determining interval a first combination of code signal components representing a` predetermined first code pattern and during a second and succeeding mode-detennininginterval a second combination of code signal components representing a predetermined second code pattern; and means for utilizing said code signal cornponents of said first combination to effect actuation of said control mechanism thereby to establish said coding apparatus throughout an interval succeeding said first mode-determining interval in one of its operating conditions determined by said first code pattern, and for utilizing said. code signal components of said second combination to effect actuation of said control mechanism for establishing said coding apparatus throughout an interval succeeding both said first and second mode-determining intervals in one of its operating conditions conjointly determined by said first and second code patterns.

9. A coding arrangement for a subscription television transmitter comprising: coding apparatus having a plurality fof operating conditions for establishing a corresponding plurality of operating modes in said television transmitter; a multi-stable actuating mechanism for said coding apparatus having at least two stable operating conditions and effectively including a plurality of electrondischarge paths cross-coupled, one to another, to render v said paths conductive one at a time in a controlled sequence; yat least three input circuits included in said actuating mechanism and individually responsive to an applied actuating signal for controlling the conductivity condition of antassigned one of said discharge paths to determine the operating condition of said actuating mechanism; means for developing during a first mode-determining interval a first combination of code signal cornponentsindividually having a .predetermined identifying frequency characteristic and collectively representing a predetermined first code pattern in accordance with their order within said first combination, and for developing during a secondand succeeding mode-determining interval a second combination of code signal components individually having a predetermined identifying t'requency characteristic and -collectively -representing a predetermined second code pattern in accordance with their order Within said second combinati-on; and means coupled to said last-mentioned means and to said input circuits for utilizing said code signal components of said first combination in a prescribed sequence to apply actuating signals to said input circuits for effecting actuation of said actuating mechanism thereby'to establish said coding apparatus throughout an interval succeeding said first mode-determining interval in one of its operating conditions determined by said first code pattern, and for utilizing said code signal components of said second combination to apply actuating signals to saidinput circuits for effecting actuation of said actuating mechanism for establishing said coding apparatus throughout an interval succeeding both said first and second vmode-determining intervals in Ione of its operating conditions conjointly determined by said first and second code patterns. Y

l10. A decoding arrangement fora subscription televi` sion receiver comprising: decoding .apparatus having a plurality of operating conditions for establishing a corresponding plurality of operating modes in said television receiver; a control mechanism. coupled to said decoding apparatus `and responsive toan applied signal for selectively actuating said decoding apparatus between its aforesaid operating conditions; means .for f developing :hiringa first mode-determining interval atfirst4 combination of code signal components-representinga predeterminedrrlstcode pattern and: duringa; second and succeeding mode-K ing said code signal components of said second combi-V nation to effect actuation of said control mechanism for establishing said decoding apparatus -throughout an in-- terval succeeding both said first and second mode-determining intervals in one of its operating conditions con-A jointly determined by said first and second code patterns.

ll. `A decoding arrangement for a subscription telef vision receiver comprising: decoding apparatus having aV plurality 'of operating conditions for establishing a corresponding plurality of operating modes in said television receiver; a multi-stable actuating mechanism for said decoding apparatus having at least two stable operating conditions and effectively including a plurality of electron-discharge paths cross-coupled, one to another, to render said paths conductive one at a time in a controlled sequence; at least three input circuits included in said actuating mechanism and individually responsive to an applied actuating signal for controlling the conductivity condition of an assigned one of said discharge paths to determine the operating condition of said actuating mechanism; means for developing during a first mode-de` termining interval a first combination of code signal cornponents individually having a predetermined identifying frequency characteristic and collectively representing a predetermined first code pattern in accordance with their order within said first combination; and for developing during a second and succeeding mode-determining inter- Y val a second combination of code signal components individually having a predetermined identifying frequency characteristic and collectively representing a predetermined second code pattern in accordance withtheir order within said second combination; and means coupled to saidv last-mentioned means and to said input circuits for utilizing said code signal components of said first cornbination in a prescribed sequence to apply actuating signals to said input circuits for effecting actuation of said actuating mechanism thereby to establish said decoding apparatus throughout an interval succeeding said first mode-determining interval in one of itsioperating conditions determined by said first code pattern, and for utilizing said code signal'components of said second combination to apply actuating signals to said input circuits for effecting actuation of said actuating mechanism for establishing said decoding apparatus throughout an interval succeeding both said first and second mode-determining intervals in one of its operating conditions conjointly determined by said first and second code patterns.

712; A method of encoding a television signal compris-v ing the steps of: developingduring a first mode-determining interval a first combination of code signal components representing a predetermined first code pattern;

utilizing said code signal components of said first combinationto establish said television signal throughout an interval succeeding said first mode-determining interval in an operating Vmode determined by said first code pattern; developing during a second and succeedingmodedetermining interval a second combination of code signal,` components *representing a predetermined second codev pattern; and utilizing said codev signal components of said second combination to establish said television signal throughout `an interval succeeding both `said first and second mode-determining intervals in an operating mode 2l conjointly determined by said rst and second code patterns.

13. A method of encoding a television signal having video-signal components in recurring field-trace intervals and synchronizing-signal components in intervening eldretrace intervals, comprising the steps of: developing during a first one of said field-retrace intervals a first combination of code signal components individually having a predetermined identifying frequency characteristic and collectively representing a predetermined first code pattern in accordance with their order within said first combination; utilizing said code signal components of said first combination to establish said television signal throughout an interval succeeding said iirst held-retrace interval in an operating mode determined by said tirst pattern; developing during a second and succeeding one of said field-retrace intervals a second combination of code signal components individually having a predetermined identifying frequency characteristic and collectively representing a predetermined second code pattern in accordance with their order within said second combination; and utilizing said code signal components of said second combination to establish said television signal throughout an interval succeeding said second field-retrace interval in an operating mode conjointly determined by said first and second code patterns.

14. An encoding device for a subscription television system comprising: encoding apparatus having a plurality of operating conditions for establishing a corresponding plurality of operating modes in said television system; a control mechanism coupled to said encoding apparatus and responsive to an applied signal for selectively actuating said encoding apparatus between its aforesaid operating conditions; means for developing during each of a series of recurring mode-determining intervals a combination of code signal components representing a code pattern; means for utilizing the code signal components developed during each of said mode-determining intervals to effect actuation of said control mechanism for establishing said encoding apparatus throughout a later interval in one of its operating conditions determined in part by the particular code pattern of such components; and means for resetting said control mechanism to establish said encoding apparatus in a predetermined reference condition at intervals recurring incommensurately with said mode-determining intervals, whereby the operating condition of said encoding apparatus is determined in accordance with the combined code patterns of more than one such combination of code signal components.

l5. An encoding device for a subscription television system comprising: encoding apparatus having a plurality of operating conditions for establishing a corresponding plurality of operating modes in said television system; a control mechanism coupled to said encoding apparatus and responsive to an applied signal for selectively actuating said encoding apparatus between its aforesaid operating conditions; means for developing during each of a .series of periodically recurring mode-determining intervals a combination of code signal components individually having a predetermined identifying characteristic and collectively representing a predetermined code pattern; means for utilizing the code signal components developed during each of said mode-determining intervals to elfect actuation of said control mechanism for establishing said encoding apparatus throughout a later interval in one of its operating conditions determined in part by the particular code pattern of such components; and means for resetting said control mechanism to establish said encoding apparatus in a predetermined reference condition at intervals recurring less frequently than said modedetermining intervals, whereby the operating condition of said encoding apparatus is determined in accordance with the combined code patterns of more than one such combination of code signal components.

16. In a subscription television system for translating 22 a television signal including video-signal components in recurring field-trace intervals and synchronizing-signal components in intervening field-retrace intervals: encoding apparatus having a plurality of operating conditions for establishing a corresponding plurality of operating modes in said television system; a control mechanism coupled to said encoding apparatus and responsive to an applied signal for selectively .actuating said encoding apparatus between its aforesaid operating conditions; means for developing during each of at least some of said iieldretrace intervals a combination of code signal components representing a code pattern; means for utilizing the code signal components developed during each of said lastmentioned field-retrace intervals to effect actuation of said control mechanism for establishing said encoding apparatus throughout a later interval in one of its operating conditions determined in part by the particular code pattern of such components; and means for resetting said control mechanism to establish said encoding apparatus in a predetermined reference condition at randomly-occurring intervals recurring less frequently than said lastentioned held-retrace intervals, whereby the operating condition of said encoding apparatus is determined in accordance with the combined code patterns of more than one such combination of code signal components.

17. In a subscription television system for translating a television signal including video-signal components in recurring field-trace intervals and synchronizing-signal components in intervening field-retrace intervals: encoding apparatus having a plurality of operating conditions for establishing a corresponding plurality of operating modes in said television system; a control mechanism coupled to said encoding apparatus and responsive to an applied signal for selectively actuating said encoding apparatus between its aforesaid operating conditions; means for developing during each of at least some of said fieldretrace intervals -a combination of code signal components representing a code pattern; means for utilizing the code signal components developed during eacl'n of said lastmentioned held-retrace intervals to effect actuation of said control mechanism for establishing said encoding apparatus throughout a later interval in one of its operating conditions determined in part bythe particular code pattern of such components; a source of reset pulses; and means coupled to said source for resetting 4said control mechanism, including means for selecting only certain ones of said reset pulses, to establish said encoding apparatus in a predetermined reference condition at intervals recurring less frequently `than said last-mentioned field-retrace intervals, whereby the operating condition of said encoding apparatus is determined in accordance with the -combined code patterns of more than one such combination of code signal components.

18. A method of operating a subscription television system comprising the steps of: developing during each of a series of recurring mode-determining intervals a combination of code signal components representing a code pattern; utilizing the code signal components developed during each of said mode-determining intervals to establish said subscription television system throughout a later interval in an lopera-ting mode determined in part by the particular code pattern of such components; and resetting said television system to a predetermined reference operating mode at intervals recurring incommensurately with said mode-determining intervals, whereby the operating mode of said system is determined in accordance with the combined code patterns of more than one such com-bination of code signal components.

References Cited in the file of this patent UNITED STATES PATENTS 2,664,461 Howland Dec. 29, 1953 2,673,238 Druz Mar. 23, 1954 2,694,105 Roschke z Nov. 9, 1954 2,697,741 Roschke Dec. 21, 1954 

